1. Field of the Invention
The present invention relates to a light emitting diode with a compound semiconductor layer stacked on a substrate, a production method thereof and a lamp.
2. Description of Related Art
As a light emitting diode (LED) capable of emitting a visible light of a red color, an orange color, a yellow color or a yellowish-green color; a compound semiconductor LED that is equipped with a light emitting layer formed of an aluminum-gallium-indium phosphide ((AlXGa1-X)YIn1-YP in which (0≦X≦1, 0<Y≦1)) has been hitherto known. In LEDs of this kind, a compound semiconductor layer having a light emitting layer made of (AlXGa1-X)YIn1-YP in which (0≦X≦1, 0<Y≦1) is generally formed on a substrate material, such as gallium arsenide (GaAs) which is optically opaque to the light emitted from the light emitting layer and does not have a high mechanical strength.
The light emitting diode described above has a device characteristic of a little current diffusion in a lateral direction. For this reason, there is a problem in that an electric current is introduced into only a region of the compound semiconductor layer immediately below an electrode and thus the light emitted from the light emitting layer is blocked by the electrode, so that the light could not be emitted to the outside. Such a light emitting diode generally has a configuration in which a translucent electrode is stacked on the compound semiconductor layer, and a metal electrode is provided on the translucent electrode, so that the light is emitted through the translucent electrode (e.g., see Japanese Unexamined Patent Application Publication No. H6-88973, Japanese Patent No. 2540791, Japanese Unexamined Patent Application Publication No. 2001-244505, Japanese Unexamined Patent Application Publication No. 2007-220709, and Japanese Unexamined Patent Application Publication No. 2008-258615). According to the light emitting diode disclosed in Japanese Unexamined Patent Application Publication No. H6-88973, Japanese Patent No. 2540791, and Japanese Unexamined Patent Application Publication No. 2001-244505, a known conductive material such as Ni/Au or ITO is used as the translucent electrode to enhance the light extraction efficiency, thereby obtaining a configuration of enhanced luminance.
However, as the light emitting diode disclosed in Japanese Unexamined Patent Application Publication No. H6-88973, Japanese Patent No. 2540791, Japanese Unexamined Patent Application Publication No. 2001-244505, Japanese Unexamined Patent Application Publication No. 2007-220709, and Japanese Unexamined Patent Application Publication No. 2008-258615, the configuration, in which the translucent electrode is stacked on the compound semiconductor layer and the metal electrode is formed thereon, has the following problems (in the description below, see FIG. 9).
First, in the case where the metal electrode is formed on the translucent electrode, when the surface of the semiconductor layer is processed to become rough state for the purpose of enhancing the light extraction efficiency, the adhesion strength between the metal electrode and the translucent electrode is likely to be deteriorated or the metal electrode is likely to be disconnected. Therefore, as described above, it is difficult to apply a technique for improving light extraction due to roughening of the surface of the semiconductor layer.
Further, since the entire metal electrode is exposed from the wafer, the metal electrode may be damaged during each process of producing the light emitting diode or a process of assembling various devices employing the light emitting diode. In particular, since the wiring electrode is formed in a simply elongated shape, the wiring electrode may be disconnected, if it is not treated properly.
In addition, in order to enhance the adhesion in the case where the metal electrode is formed on the translucent electrode, a metal thin film layer, for example, a Cr layer or a Ti layer, for enhancing the adhesion is generally formed at an interface. However, since the Cr layer or the like has a property of easily absorbing the light, in the case where the Cr layer or the like is formed on the translucent electrode, the light extraction efficiency of the light emitting diode is deteriorated, and the added process causes an increase in cost.